Abrasion resistant electric cable



Oct. 14, 1952 W H- BENTON, JR 2,614,147

ABRASION RESISTANT ELECTRIC CABLE Filed July 2, 1949 BY Kwak@ um 'ap/5MM ATTORNEYS Patented Oct. 14, 1952 ABRASION RESISTANT ELECTRIC CABLE William H. Benton, Jr., Marion, Ind., assignor to Anaconda Wire and Cable Company, a corporation of Montana Application July 2, 1949, Serial No. M2352 2 Claims.

This invention is directed particularly to the provision of an improved multiconductor electric cable in which separately insulated conductors are mechanically interlocked so as to restrain them against lateral displacement of one from the other when subjected to severe mechanical distorting forces. The cable of the invention is of a particularly advantageous design for supplying power to electrically operated coal mining machinery and related apparatus, but of course it may be used for many other purposes as well.

The cable of the invention comprises at least two insulated conductors, the insulation about one of such conductors being formed with a longitudinal tongue extending throughout the length thereof, and the insulation about the other of such conductors being formed with a corresponding longitudinal groove. In the completed cable, the two conductors are laid together side by side, and are interlocked by projection of tongue into the groove. Binding means secure the insulated conductors together in such tongue and groove interlocked position, whereby they are restrained against lateral displacement of one from the other even when the cable is subjected to severe mechanical abuse.

The invention is particularly easily and advantageously incorporated in a cable structure comprising two conductors each of which is surrounded by avlayer of insulation substantially D-shaped in cross section. In such a cable, the flat of one of the D-shaped layers of insulation is provided with the tongue, and the flat of the other of such layers is provided with the corresponding groove.

Any type of binding may be used to secure the insulated conductors together. In cables intended for rugged service (as in supplying power to mining machinery), it is desirable to apply a jacket of insulating material about the assembled insulated conductors, and such jacket alone may serve as the binding, or it may be reinforced with binding cords or threads embedded in it, or underlying it, or surrounding it. For convenience in manufacturing the cable, however, it is generally desirable to apply binding cords or threads directly about the assembled and interlocked insulated conductors, and then to extrude the jacket of insulating material about the resulting assembly. The binding cords in such case hold the insulated conductors tightly together during the operation of applying the jacket, and serve to reinforce the binding effect of the jacket in the completed cable.

In order to enhance the ability of the cable to withstand rough hand-ling and other mechanical abuse, it is advantageous to interpose between the two insulated conductors a breaker strip comprising a strip of fabric material shaped so that one face conforms with the tongue formed on one of the layers of conductor insulation and so that its opposite face conforms with the groove provided in the layer of insulation about the other conductor. For maximum ruggedness of construction, all of the components of the cable are advantageouslyadhesively bonded together, as described and claimed in the R. A. Johnson United States Patent No. 2,455,773, dated December 7, 1948.

Advantageous embodiments of cable made in accordance with the invention are shown in the accompanying drawing, wherein:

Fig. 1 shows in cutaway perspective a cable having two separately insulated conductors interlocked by a single tongue and groove; and

Fig. 2 shows a similar cable having the separately insulated conductors interlocked by a plurality of tongues and grooves.

The cable shown in Fig. 1 comprises a pair of copper conductors 5 and 6 surrounded by layers I and 8, respectively, of rubber or other iiexible insulating material. These insulating layers are substantially D-shaped in cross section, and are most conveniently formed by extrusion about the conductor. The iiat (that is, the surface 9) of one of the D-shaped layers of insulation I is formed with a longitudinal groove I0 extending throughout its length, and the iiat of the other layer of insulation 8 is formed with a corresponding tongue II. The insulated conductors are assembled side by side together with their respective flats facing each other, so that the tongue I I projects into the groove Ill.

Interposed between the insulated'conductors are a pairl of breaker strips I2, each of which comprises a strip of fabric and each of which advantageously is impregnated with rubber or other insulating material. One side face of each breaker strip I2 is shaped to conform substantially with the grooved Iiat of the layer of insulation 1, and the opposite face thereof is correspondingly shaped to conform substantially with the tongued fiat of the other layer of insulation 8,

The insulated conductors are held together side by side in tongue and groove interlocked position by an open braid I3 of cotton threads or other binding material, and by an overall jacket I4 of rubber or other iiexible material. With the Insulated conductors thus interlocked and bound together, the assembled cable is able to withstand very large torsional and longitudinal shear forces without suffering lateral displacement of the conductors one from the other. Thereby the cable is enabled to resist considerably greater mechanical abuse than heretofore conventional cables not having the separately insulated conductors mechanically interlocked throughout their lengths.

The purpose of the breaker strips l2 is to reduce the likelihood of a short circuit between the conductors 5 and 6 in case the cable is subjected to a severely applied compressive force or shear force acting laterally of the cable and of sufficient magnitude to cause the conductors to out through the layers of insulation 'I and 8. For many types of service only one breaker strip, instead of the two shown in Fig. l, is sufficient; and indeed the breaker strips may be omitted altogether without departing from the invention. f

All of the components of the cable may be adhesively bonded together by lms of rubber cement or other adhesive in order further to increase resistance or the cable to mechanical abuse, as described in the aforementioned J ohnson Patent No. 2,455,77 3. Alternatively, in cables where ease of longitudinal adjustment of the insulated conductors relative to each other is of importance to secure maximum flexibility, the breaker strips and conductor insulation layers may be lubricated with soapstone, graphite, a wax, or other lubricant. Even when a lubricant is used the tongue and groove interlocking between the layers of insulation prevents lateral displacement of one from the other.

A modified form of cable according to the invention is shown in Fig. 2. In this modification, as in the cable previously described, a pair of stranded conductors and 2i are surrounded by layers of insulation 22 and 23, respectively. The layers of insulation are substantially D- shaped in cross section, and that surface of each of such layers corresponding to the fiat of the D is serrated, so that one of such layers is provided with a tongue 24 midway between a pair of grooves 25, and the other insulating layer 23 is provided with a groove 28 midway between a pair of tongues 2l. The insulated conductors are assembled together side by side so that the central tongue 211 of the insulating layer 22 engages in the central groove 26 of the other in sulating layer 23, and the flanking tongues 2'! engage in the corresponding flanking grooves 25. The resulting tongue and groove interengagement between the two insulated conductors extends throughout the length of the cable.

As in the case of the cable shown in Fig. l, the insulated conductors are bound together by an open braid 28 of cotton threads or the like, and by an outer protective jacket 29. The layers of insulation and the jacket may all be adhesively bonded to each other, as previously described, or alternatively, where maximum exibility is required, a lubricant may be used between the interlocked layers of insulation.

Cables made in accordance with the invention are readily manufactured to close dimensional tolerances without fear of inadequate insulation between the conductors at any point throughout the length of the cable, because it is not diflcult to maintain each conductor properly centered while its individual layer of insulation is being extruded thereon. At the same time, the overall ability of the new cable to resist mechanical abuse is substantially equal to that of a cable in which the two conductors are embedded in an integral layer of insulation, or is even superior thereto when breaker strips are incorporated in the structure. The tongue and groove interlocking between the separately insulated conductors renders them substantially as resistant to lateral displacement as when a single integral layer of insulation surrounds and separates them, and avoids the need for relying on an adhesive bond between separate layers of insulation to prevent such displacement.

I claim:

l. An electric cable comprising at least two insulated conductors, the insulation about one of said conductors being formed with a longitudinal tongue and the insulation about the other of said conductors being formed with a corresponding longitudinal groove, said two insulated conductors being laid together side by side and being interlocked by projection of said tongue into said groove, a layer of lubricant between the interlocking faces of said insulated conductors, and means binding the insulated conductors together in such interlocked position, said means being adhesively secured to said conductors throughout its length, whereby the insulated conductors are restrained against lateral displacement of one from the other but some 1ongitudinal relative movement is permitted their interlocked faces.

2. An electric cable comprising a pair of conductors each surrounded by a layer of insulation substantially D-shaped in cross section, the fiat of one of said layers being formed with a longitudinal tongue and the nat of the other of said layers being formed with a corresponding longitudinal groove, said insulated conductors being laid together with their flats facing each other and being interlocked by projection of said tongue into said groove, a layer of lubricant between the flats of said insulated conductors, and a jacket surrounding the pair of insulated conductors and holding them together in such interlocked position, said jacket being adhesively secured to said conductors throughout its length, `whereby the insulated conductors are restrained against lateral displacement of one from the other but some longitudinal. relative movement is permitted their interlocked fiat faces.

WILLIAM H. BENTON, Jn.

REFERENCES CITED The following references are of record in the file of this patent: A

UNITED STATES PATENTS Number Name Date 1,900,976 Carpe et al. Mar. 14, 1933 1,957,487A Buckley et al. May 8, 1934 2,031,634 McblarneeY May 25, 1937 2,455,773 Johnson Dec. 7, 1948 FOREIGN PATENTS I Number Country Date 153,118 Switzerland Feb. 29,1932 381,038 England Sept. 29, 1932 

